Sculpting tools don't seem to work unless using remesh or dyntopo
I was able to sculpt when I applied the two modifiers (mirror &amp; sub) and filled the holes in Edit Mode (select all + f for fill). I don't know enough about the sculpt tools but maybe brushes like crease need closed meshes. Depending on what you want to do don't expect high resolution and details without Dyntopo on this one.